Linear hydraulic motors



Oct. 21, 1969 D. FIRTH ETAL LINEAR HYDRAULIC MOTORS 9 Sheets-Sheet 1 Filed Dec. '7. 1967 FIG, 4. /04 02 Oct. 21, 1969 D. FIRTH ET AL LINEAR HYDRAULIC MOTORS 9 Sheets-Sheet 5 Filed Dec. '7, 1967 Oct. 21, 1969 D. FIRTH ETAL 3,473,440

LINEAR HYDRAULIC MOTORS Filed Dec. '7, 1967 9 Sheets-Sheet 4 S5 3% 5% ww H14 /f/ //////l Filed Dec. 7. 1967 9 Sheets-Sheet 5 FIG. 6.

FlJ22 Oct. 21, 1969 D. FIRTH ETAL 3,473,440

LINEAR HYDRAULIC- MOTORS Filed Dec. 7. 1967 9 Sheets-Sheet 7 Oct. 21, 1969 D. FIRTH 51m. 3,473,440

LINEAR HYDRAULIC IO'I'ORS Filed Dec. 7, 1967 9 Sheets-Sheet 8 I I 242 l l l FIG.9.

Oct. 21, 1969 D. FIRTH ETAL 3,473,440

LINEAR mmmmuc mo'rons Filed Dec. '7, 1967 9 Sheets-Sheet 9 FIG. 70.

lU-S. Cl. 91-176 12 Claims ABSTRACT (IF THE DISCLGSURE A linear hydraulic motor of the ball and cam-track type in which the pressure applied to the balls is controlled in accordance with the relative position of the motor and track by a fluid pressure senser device co-operating with lands and grooves associated with the track.

This invention relates to fluid-operated motors.

An object of the present invention is the provision of improved means for operating the fluid supplying and exhausting valve means of a fluid operated motor, particularly a linear motor, which term includes arcuate motors.

According to one aspect of the invention a fluidoperated motor comprises a number of cylinders containing pistons, the pistons being adapted to bear against a track in the form of a repetitive cam surface, means for supplying operating fluid under pressure to the cylinders selectively, and means to control the supply of fluid including a sensing device which includes a fluid discharge nozzle adapted to discharge the fluid against a baflie associated with the cam surface, the baffle being relieved at predetermined positions whereby fluid pressure upstream of the nozzle is reduced when the nozzie is adjacent to the relieved portions thus producing a pressure signal dependent on the position of the pistons relatively to the cam surface, the pressure signal being applied to valve means controlling supply of the pressurised fluid to the cylinders in such a manner as to produce relative movement between the portion of the motor including the cylinders and the cam surface.

The invention has particular application to ball motors. In such motors the movement of a shaft secured to the carrier for the balls can easily be used to control the supply of hydraulic fluid to, and the venting of hydraulic fluid from the space between the pair of balls, but in the case of a linear ball motor it has been considered necessary to utilise a rotary valve driven by a gear wheel carried by the moving carrier and engaging a fixed rack associated with the cam surfaces. Such a rack is not easy to provide and is not easy to maintain in good condition, being liable to fouling with dirt including grit which can upset the engagement of the gear Wheel with the rack. A friction drive to the rotary valve is impractical since cumulative slippage would in time cause the admission and exhaust of the hydraulic fluid to take place at the wrong relative positions of the balls and the cam surfaces.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a perspective drawing indicating schematically, but not in detail a linear hydraulic ball motor operating in a cam track and associated with body moved relative to the track by the motor;

FIGURE 2 is a transverse section through the track and the motor shown in FIGURE 1;

ite States Patent FIGURE 3 is a sectional front elevation taken on the line IIIIII of FIGURE 2.

FIGURE 4 is a sectional front elevation taken on the line IV-IV of FIGURE 2;

FIGURE 5 is a sectional plan view taken on the line VV of FIGURE 2;

FIGURE 6 is a schematic representation of a hydraulic system parts of which are shown in FIGURES 3 to 5;

FIGURE 7 shows schematically the control system of an alternative form of motor embodying the invention;

FIGURE 8 is an end elevation of the motor incorporated in FIGURE 7;

FIGURE 9 is a section line IX-IX of FIGURE 8; and

FIGURE 10 is an under plan of the motor shown in FIGURES 8 and 9.

In FIGURE 1, the linear hydraulic motor 1 co-operates with a cam track 3 (indicated diagrammatically only) and serves to move a body 5 (indicated merely as a dotted outline) along the length of the track. For the purposes of the present invention the actual form of the body 5 is unimportant, and all that it is necessary to note is that the body is supported and guided independently of the track 3, and the only function of the motor is to supply a force on the body 5 in a direction along the track indicated by the arrow 7.

As indicated in FIGURE 1, and shown more clearly in FIGURES 2 and 3, the cam track 3 is in the form of a slot 9 formed in and extending horizontally along a massive first member 11, which can be of steel in the case of a relatively short and/or small track but which can be formed of concrete in a relatively large motor system. The upper surface 13 and the lower surface 15 of the slot 9 are sinuously curved as can be seen in FIGURE 3, the phase of these curved surfaces being such that the valleys and the crests in the surface 13 are respectively opposite the valleys and the crests in the surface 15.

The motor 1 includes a rectangular body 21 the height of which is slightly less than the height of the slot 9, and part of which extends into that slot. The part of the body 21 within the slot is formed towards each of its two ends with a group of four cylinders, 31, 32, 33 and 34 arranged with their axes vertical and accommodating respectively a pair of balls 41, a pair of balls 42, a pair of balls 43 and a pair of balls 44. These balls are a closesliding fit in their associated cylinders, and the pair of balls in each cylinder act as opposed pistons which can be forced apart by hydraulic fluid supplied under pressure through ports 51, 52, 53 and 54 respectively. The axes of the four cylinders 31, 32, 33 and 34 are displaced relative to one another along the length of the body 21, being distributed over a length of the body equal to threequarters of the pitch of the profile of each of the cam surfaces 13 and 15.

The ports 51, 52, 53 and 54 serve also for the exhaust of hydraulic fluid from the cylinders, and the general principles of operation of the linear hydraulic motor is that as hydraulic fluid is supplied to, and exhausted from, the various cylinders in each group in proper sequence, the reaction set up between the balls and the cam surfaces 13 and 15 will produce a linear force on the motor body 1 in the direction of the arrow 7, either to the left or to the right in FIGURE 3, and it is possible in practice to arrange for this force to remain constant with a constant oil pressure as the motor body 21 and the body 5 move along the track. Each group of four cylinders produces a constant force, and although two groups are mentioned, four or more could be used.

FIGURES 4 and 5 illustrate the manner in which valves for the supply and exhaust of hydraulic fluid to the various cylinders are controlled, and FIGURE 6 illustrates the hydraulic circuit including these valves. Disposed respectively in four horizontal bores in a central part of the motor body 21 are four spool valves 61, 62, 63 and 64, the inlet/exhaust ports 51, 52, 53 and 54 of the associated cylinder communicating with ports pro vided at the mid-point of the length of the associated bore. The body on which the motor 1 is provided houses a motor 81 driving a hydraulic pump 83 of the swash plate type, the setting of the pump swash plate determining the direction of flow of hydraulic fluid in a closed circuit including hydraulic fluid pipes 87 and 89 associated respectively with hydraulic fluid passages 97 and 99 formed in the motor body 21. Each of the valve bores is provided with a pair of ports, arranged respectively to the two sides of the mid-length port. Each spool-valve is so dimensioned that in one limiting axial position it blocks the port associated with passage 97 but permits communication between the port associated with the passage 99 and the mid-length port, while in its other limiting axial position it blocks the port associated with passage 99 but permits communication between the port associated with passage 97 and the mid-length port.

Operation of the spool valves 61, 62, 63 and 64 takes place automatically in accordance with the position of the motor 1 along the track 3. This automatic operation is brought about by the interaction of discharges of hydraulic fluid from four nozzles 102, 104, 106 and 103 formed in a block 111 carried by the motor body 21 with an adjacent surface 113 of the member 11. The upper part of the surface 113 is formed with recesses 115 each having a length equal to half the pitch of the profile of the cam surfaces 13 and 15 and spaced from each of the adjacent recesses by an equal distance. The nozzles terminate in very small orifices in a face 11A of the block 111 which is very close to the surface 113, and the four nozzles are evenly spaced apart over a distance equal to three-quarters of that pitch with the four nozzles lying respectively in the four transverse planes containing the axes of the four cylinders. Hydraulic fluid is supplied to these nozzles from a duct 117 through separate flow restrictors 119A, 119B, 119C and 1191) while the part of each nozzle between its flow restrictor and its outlet orifice communicates by a duct 122, 124, 126, or 128 to a first end of one of the spool valve bores and to a second end of another of the spool valve bores. Thus nozzle 102 is connected to a first end of the bore of spool valve 64 and to a second end of the bore of spool valve 62; nozzle 104 is connected to a first end of the bore of spool valve 63 and to a second end of the spool valve 61; nozzle 106 is connected to the second end of the bore spool valve 64 and to the first end of the bore of spool valve 62; and nozzle 108 is connected to the second end of the bore of spool valve 63 and to the first end of the bore of spool valve 61. Each of the spool valves acts as a bistable element, and will adopt one or the other of its limiting axial positions depending upon which of the pressures applied respectively to the two ends of the bore is the greater.

When o he of the nozzles is opposite one of the recesses 115, the fluid pressure in the nozzle is considerably less than in the case when the nozzle is opposite a part of the wall between two of the recesses 115. Thus with the parts in the position shown in FIGURE 5, the pressure in nozzle 106 and 108 is greater than the pressure in nozzles 102 and 104. As a result, the valve spools will adopt the position shown in FIGURE 6. Under these conditions, if the pump 83 is set to produce a fluid flow from the pump into pipe 87 then hydraulic fluid is fed into the cylinders 33 and 34 and is exhausted from cylinders 31 and 32. This will produce a force on the body 21 of the motor towards the left in FIGURE 3. After a short travel of the motor body 21, the nozzle will lie opposite a recess 115 and the nozzle 104 will lie opposite a land between two recesses. Thus the pressure in nozzle 104 and 106 will be high and the pressure in nozzles 108 and 102 will be low. This will cause spool valves 61 and 63 to change their stable states, so that hydraulic fluid is supplied under pressure to cylinders 31 and 34 and so that hydraulic fluid can be exhausted from cylinders 32 and 33. This also will produce on the motor body 21 a force tending to move it towards the left in FIGURE 3. Further study of the action of the hydraulic system will make it clear that this movement to the left will continue. it will also be seen that a reversal of the swash plate of the pump 83 will not affect the positions of the spool valves but will reverse the conditions of supply and exhaust of hydraulic fluid relative to the cylinders, and so will produce a reverse movement of the motor body 21, i.e. to the right in FIGURE 3.

It will be seen that by the arrangement set out above automatic operation of the valve means for the supply of hydraulic fluid to the cylinders of the linear hydaulic motor is ensured and yet no mechanical device such as a rack and pinion is utilised. This considerably improves the freedom from impairment in operation which could otherwise follow the ingress of dirt into the mechanism.

In the preferred embodiment described above the fluid supplied to the nozzles 102, 104, 106 and 108 was hydraulic fluid, and although this is quite practical in the case of a motor which is used in a machine tool or the like where the discharged liquid can be recovered, in the case of a linear motor used for outdoor use it would be more practical to utilise a gas under pressure as the working fluid in these nozzles. There would then be no need to bother about recovery of this fluid, and this permits application of the invention to a much larger range of situations.

For some applications of the invention, e.g. in the operation of machine tool slides, it may be more convenient if the motor 1 is stationary and the cam surfaces are provided on the slide which it is required to move.

The linear ball motor can be used in servo-control applications, and in such an application the hydraulic power may be supplied by a constant pressure pump. An electrohydraulic flow control valve would then be used in the supply line to control the direction and speed of the motor.

The motor shown in FIGURES 8, 9 and 10 comprises a body 200 within which is mounted a cylinder block 202 having eight circular rows of cylinders 204, 206, 208, 210, 212, 214, 216 and 218 (FIGURE 9). Each row of cylinders may comprise any number of radially directed cylinders, each containing a piston which may be in the form of a ball or a cylindrical piston with a spherical follower. In the example shown in the drawing there are sixteen cylinders in each of the eight rows, each cylinder contains a piston in the form of a ball. Thus each cylinder 204 contains a ball 224 and the cylinders 206, 208, 210, 212, 214, 216 and 218 certain respective balls 226, 228, 230, 232, 234, 236 and 238.

The balls bear against a repetitive cam surface 240 formed on a ram 242 located coaxially within the cylinder block 202. As illustrated, the ram 242 is axially movable, the body 200 and cylinder 202 being held stationary and the body or ram made movable. The ram 242 is prevented from rotating relatively to the cylinder 202 by keys 244 and 246 which engage respective keyways 248 and 250.

The cylinders 204, 206 etc., are supplied with operating fluid, which may be oil under pressure, through a pair of spool valves 252, 254 the movements of which are controlled by a senser device 256 containing a pair of sensers 258, 260.

The direction of movement of the ram 242 is controlled by a control valve 262 (FIGURE 8).

The general operation of the system will now be described with reference to FIGURE 7 after which the details of the motor will be described.

In FIGURE 7 is shown a pump 264 which circulates operating fluid via control valve 262 to spool valves 252 and 254 and thence selectively to the cylinders 204 etc. Only four rows of cylinders 204, 206, 208 and 210 are 

